70 
PKOEESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
Of the dentition of this jaw, I commence the description with those in that of the 
immature specimen of Not other ium Mitclielli (Plate VI.), consisting of the right 
ramus of the mandible with the first three molars in place, the germ of a fourth, and 
part of the formative cavity of a fifth molar. The tip of a procumbent incisor projects 
from a socket, close to the symphysis, where sufficient of the cavity was exposed to 
show that it expanded as it sank in the substance of the jaw. 
Putting aside for awhile the evidence of the nature of this specimen afforded by 
others since received from Australia, I believe it may be of some interest and instructive- 
ness to show how far its determination can be carried on the supposition that it is the 
sole example of its kind. 
The mammalian character is seen at a glance by the complex crowns and rooted 
implantation of the molars, and by the simple condition of the ramus of the jaw, as 
of one piece of bone. The nonage of the individual to which the jaw has belonged 
is recognized at the same moment. 
Of Mammalia corresponding in size with the parent of a young one having its newly 
cut milk-series of teeth in a jaw 8 inches long, the number of genera is not great ; and 
we may be excused for thinking that most of those which are now represented by living 
species must be known. Of these we should be led at once to Cuvier’s Pachyderms by 
the shape and size of the teeth of our young giant. The broad complex crowns of the 
molars show its herbivorous nature. The Tapir alone exhibits the bilopliodont type of 
the second and third milk-grinders, with the conical, partly trenchant, partly crushing 
shape of the first ; but it developes, with these in the mandible, eight small front teeth, 
of which the outermost pair are canines. A Rhinoceros of Sumatra or Java may show 
a pair of large tusk-like lower incisors, but they are associated, in the milk-dentition, 
with a smaller pair of mid incisors*. 
There is another and more significant difference which the present fossil evidence of 
a large Herbivore presents in comparison with a specimen of the same age, or with the 
same phase of dentition, of any existing Herbivore. In the young Tapir, e. g., with three 
deciduous molars in each mandibular ramus, and the germ of the next molar lying in 
its formative cavity deeper and less advanced than in the present fossil, the enamel 
has been worn from the summits of the first and second milk-molars so far as to expose 
the dentine, and it is abraded obliquely backward from the summits of both ridges of 
the third molar. 
So also in a young Rhinoceros in which the second and third milk-molars are in place, 
the first and fourth being still “ en germe ,” the enamel shows masticatory abrasion at the 
summits of the two chief lobes of H and d 3. Corresponding signs of the assumption 
of vegetable nutriment in addition to that afforded by the mother’s milk are visible in 
young Equines and Ruminants with a stage of molar dentition corresponding to that 
shown by the fossil under consideration. 
Now here, although the first, second, and third molars are well in place, and the 
* Owen’s ‘ Odontography,’ p. 591, pi. 138. fig. 15, cli, 1 & 2. 
